Computer assisted knee replacement

Radiographic and navigation measurements of TKA limb alignment do not correlate

Precise pre- and postoperative anatomic measurements are necessary to plan, perform, and evaluate total knee arthroplasty (TKA). We evaluated the relationship between radiographic and navigation alignment measurements, identified sources of error in radiographic and navigated alignment assessment, and determined the differences between desired and clinically accepted alignment. Fifty-eight computer-assisted TKAs were performed and limb alignment measurements were recorded both pre- and postoperatively with standard radiographs and with an intraoperative navigation system. Intraoperative navigation produced consistent navigation-generated alignment results that were within 1 degrees of the desired alignment. The difference between preoperative radiographic and navigation measurements varied by as much as 12 degrees and the difference between postoperative radiographic and navigation measurements varied by as much as 8 degrees. This discrepancy depended on the degree of limb deformity. Postoperative radiographic measurements have inherent limitations. Navigation can generate precise, accurate, and reproducible alignment measurements. This technology can function as an effective tool for assessing pre- and postoperative limb alignment and relating intraoperative alignment measurements to clinical and functional outcomes.

LEVEL OF EVIDENCE

Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Results of an initial experience with custom-fit positioning total knee arthroplasty in a series of 48 patients

The custom-fit approach to total knee arthroplasty in conjunction with removal of osteophytes and preservation of ligaments rapidly returned function; restored motion, stability, and postoperative mechanical axis alignment; effected high patient satisfaction; and had an acceptable clinical outcome.

Navigated unicompartmental knee replacement

Computer-aided systems have been developed recently to improve the precision of implantation of unicompartmental knee replacement (UKR) or total knee replacement. Minimal invasive techniques have been developed to decrease the surgical trauma related to the prosthesis implantation. However, there might be a concern about the potential of minimal invasive techniques for a loss of accuracy. Navigation systems might address this issue. We are currently using routinely a nonimage-based navigation for total knee replacement. We developed a modified system for UKR, suitable for either a conventional or a mini-invasive approach. Navigated implantation of a UKR allowed improving the accuracy of the radiologic implantation. Mini-invasive implantation was effective, but the accuracy may not reach that of the conventional navigated technique and should be still improved. Minimal invasive techniques have to be validated because a loss of accuracy will negatively influence long-term outcomes.

Improved accuracy of component alignment with the implementation of image-free navigation in total knee arthroplasty

Accuracy of implant positioning and reconstruction of the mechanical leg axis are major requirements for achieving good long-term results in total knee arthroplasty (TKA). The purpose of the present study was to determine whether image-free computer navigation technology has the potential to improve the accuracy of component alignment in TKA cohorts of experienced surgeons immediately and constantly. One hundred patients with primary arthritis of the knee underwent the unilateral total knee arthroplasty. The cohort of 50 TKAs implanted with conventional instrumentation was directly followed by the cohort of the very first 50 computer-assisted TKAs. All surgeries were performed by two senior surgeons. All patients received the Zimmer NexGen total knee prosthesis (Zimmer Inc., Warsaw, IN, USA). There was no variability regarding surgeons or surgical technique, except for the use of the navigation system (StealthStation) Treon plus Medtronic Inc., Minnesota, MI, USA). Accuracy of implant positioning was measured on postoperative long-leg standing radiographs and standard lateral X-rays with regard to the valgus angle and the coronal and sagittal component angles. In addition, preoperative deformities of the mechanical leg axis, tourniquet time, age, and gender were correlated. Statistical analyses were performed using the SPSS 15.0 (SPSS Inc., Chicago, IL, USA) software package. Independent t-tests were used, with significance set at P < 0.05 (two-tailed) to compare differences in mean angular values and frontal mechanical alignment between the two cohorts. To compute the rate of optimally implanted prostheses between the two groups we used the chi(2) test. The average postoperative radiological frontal mechanical alignment was 1.88 degrees of varus (range 6.1 degrees of valgus-10.1 degrees of varus; SD 3.68 degrees ) in the conventional cohort and 0.28 degrees of varus (range 3.7 degrees -6.0 degrees of varus; SD 1.97 degrees ) in the navigated cohort. Including all criteria for optimal implant alignment, 16 cases (32%) in the conventional cohort and 31 cases (62%) in the navigated cohort have been implanted optimally. The average difference in tourniquet time was modest with additional 12.9 min in the navigated cohort compared to the conventional cohort. Our findings suggest that the experienced knee surgeons can improve immediately and constantly the accuracy of component orientation using an image-free computer-assisted navigation system in TKA. The computer-assisted technology has shown to be easy to use, safe, and efficient in routine knee replacement surgery. We believe that navigation is a key technology for various current and future surgical alignment topics and minimal-invasive lower limb surgery.

Passive knee kinematics before and after total knee arthroplasty: are we correcting pathologic motion?

The change in coronal plane deformity throughout a range of flexion before and after total knee arthroplasty (TKA) has not been reported. Unlike most alignment assessments traditionally reporting coronal plane alignment in a standing position under static conditions, this study reports deformity throughout the flexion arc before and after deformity correction. One hundred fifty-two TKA patients using the anteroposterior axis for femoral component rotation and computer navigation techniques were included in the study. Deformity before TKA ranged from 17.5 degrees varus (deformity apex away from the midline) to 20.5 degrees valgus (deformity apex toward the midline) in full extension. Before TKA, deformity was not constant through an arc of motion and significantly decreased with flexion of 60 degrees and more (P < .01). The deformity after performing a TKA was not different (P = .478) throughout the flexion arc. The data determined that deformity is not constant throughout flexion in osteoarthritic knees preoperatively and that deformity throughout flexion can be corrected with the use of conventional alignment techniques during TKA.

Computer-assisted total knee arthroplasty versus the conventional technique: how precise is navigation in clinical routine?

Restoration of the mechanical leg axis and component positioning are crucial factors affecting long-term results in total knee arthroplasty (TKA). In a prospective study, 1,000 patients were operated on either using a CT-free navigation system or the conventional jig-based technique. Leg alignment and component orientation were determined on postoperative X-rays. The mechanical leg axis was significantly better in the computer-assisted group (95%, within +/-3 degrees varus/valgus) compared to the conventional group (74%, within +/-3 degrees varus/valgus) (P < 0.001). On average, the operating time was increased by 8 min in the computer-assisted group. No significant differences were seen between senior and younger surgeons regarding postoperative leg alignment and operating time. Computer-assisted TKA leads to a more accurate restoration of leg alignment and component orientation compared to the conventional jig-based technique. Potential benefits in long-term outcome and functional improvement require further investigation.

Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery

Computer-assisted surgery (CAS) has been advocated as a means to improve limb and prosthesis alignment and assist in ligament balancing in total knee arthroplasty (TKA). Thus, we sought to examine alignment outcomes in CAS vs conventional TKA. A systematic review of literature from 1990 to 2007 was performed. Direct comparison of alignment outcomes was performed using random effects meta-analyses. Twenty-nine studies of CAS vs conventional TKA were identified, and included mechanical axis malalignment of greater than 3 degrees occurred in 9.0% of CAS vs 31.8% of conventional TKA patients. The risk of greater than 3 degrees malalignment was significantly less with CAS than conventional techniques for mechanical axis and frontal plane femoral and tibial component alignment. Tibial and femoral slope both showed statistical significance in favor of CAS at greater than 2 degrees malalignment. Meta-analysis of alignment outcomes for CAS vs conventional TKA indicates significant improvement in component orientation and mechanical axis when CAS is used.

Navigated non-image-based positioning of the acetabulum during total hip replacement

We tested the hypothesis that the non-image-based navigation system used in our department was able to measure accurately the 3D positioning of the acetabular cup of a total hip replacement (THR) and to increase the accuracy of its implantation during THR. We studied 50 consecutive navigated implantations of a THR and compared the intra-operative measurement of the cup by the navigation system to the post-operative measurement by computed tomography (CT) scan. The mean difference between the navigated and CT scan measurements for cup inclination was 2 degrees . The mean difference between the navigated and CT-scan measurements for cup flexion was 4 degrees . These differences were significant but considered to be clinically irrelevant in most cases. A total of 73% of the cases were within the safe zone defined prior to the study. The non-image-based system used allows a precise orientation of the cup during THR.

A quantitative method of effective soft tissue management for varus knees in total knee replacement surgery using navigational techniques

Total knee replacement (TKR) has become the standard procedure in management of degenerative joint disease with its success depending mainly on two factors: three-dimensional alignment and soft-tissue balancing. The aim of this work was to develop and validate an algorithm to indicate appropriate medial soft tissue release during TKR for varus knees using initial kinematics quantified via navigation techniques. Kinematic data were collected intra-operatively for 46 patients with primary end-stage osteoarthritis undergoing TKR surgery using a computer-tomography-free navigation system. All patients had preoperative varus knees and medial release was made using the surgeon's experience. Based on these data an algorithm was developed. This algorithm was validated on a further set of 35 patients where it was used to define the medial release based on the kinematic data. The post-operative valgus stress angles for the two groups were compared. These results showed that the algorithm was a suitable tool to indicate the type of medial release required in varus knees based on intra-operatively measured pre-implant valgus stress and extension deficit angles. It reduced the percentage of releases made and the results were more appropriate than the decisions made by an experienced surgeon.

Using navigation intraoperative measurements narrows range of outcomes in TKA

Computer-assisted technology creates a new approach to total knee arthroplasty (TKA). The primary purpose of this technology is to improve component placement and soft tissue balance. We asked whether the use of navigation techniques would lead to a narrow range of implant alignment in both coronal and sagittal planes and throughout the flexion-extension range. Using a prospective consecutive series of 57 navigated TKAs, we assessed intraoperative knee measurements, including alignment, varus-valgus stress angles in extension, and varus-valgus angles from 0 degrees to 90 degrees of flexion comparing postimplant with preimplant. We found fewer outliers with coronal (100% of TKAs within +/-2 degrees) and sagittal (0% of TKAs with fixed flexion greater than 5 degrees) alignment, soft tissue balancing (mean varus and valgus stress angles -3.2 degrees and 2.3 degrees; range, -5 degrees to 5 degrees), and mean femorotibial angle over flexion range 0 degrees (-0.2 degrees; range, -1 degrees to 2 degrees), 30 degrees (-0.2 degrees; range, -5 degrees to 4 degrees), 60 degrees (-0.5 degrees; range, -5 degrees to 7 degrees), and 90 degrees (-0.2 degrees; range, -5 degrees to 10 degrees). This technology allows a narrow range of implant placement and soft tissue management in extension. We anticipate improved ultimate patient outcomes with less tissue disruption.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

The rationale for navigated minimally invasive unicompartmental knee replacement

Computer-aided systems have been developed recently to improve the precision of implantation of unicompartmental or total knee replacements. Minimally invasive techniques were developed to decrease the surgical trauma related to prosthesis implantation. However, there are concerns about loss of implant positioning accuracy with minimally invasive techniques. Minimally invasive instruments have been adapted for use with a typical 6-cm skin incision for unicompartmental knee replacement. We prospectively studied 60 patients who had minimally invasive navigated UKA and compared them with an earlier group of 60 patients who underwent open navigated UKA. We used an intraoperative non-image-based navigation system. Minimally invasive navigated implantation of a UKA did not reduce the radio-graphic accuracy of the implantation compared to open navigated implantation. There were no major complications and little change from the conventional navigated operating technique. Because we do not yet know if navigation influences function and long-term survival, our conclusions need to be confirmed on a larger scale.

Coronal plane stability before and after total knee arthroplasty

The success of total knee arthroplasty depends in part on proper soft tissue management to achieve a stable joint. It is unknown to what degree total knee arthroplasty changes joint stability. We used a surgical navigation system to intraoperatively measure joint stability in 24 patients under going primary total knee arthroplasty to address two questions: (1) Is the total arc of varus-valgus motion after total knee arthroplasty different from the arc of varus-valgus motion in an osteoarthritic knee? (2) Does total knee arthroplasty produce equal amounts of varus/valgus motion (ie, is the knee "balanced")? We observed no difference between the total arc of varus-valgus motion before and after total knee arthroplasty; the total amount of motion was unchanged. On average, osteoarthritic knees were "unbalanced" but were "balanced" after prosthesis implantation. We found a negative correlation between the relative amount of varus/valgus motion in extension before and after prosthesis implantation in extension and a positive correlation between how well the knees were balanced after prosthesis implantation in extension and in flexion. Our data suggest immediately after implantation knees retain a greater than normal amount of varus-valgus motion, but this motion is more evenly distributed.

Alignment of resection planes in total knee replacement obtained with the conventional technique, as assessed by a modern computer-based navigation system

BACKGROUND

To improve the anatomy-based alignment of prosthetic components in total knee replacement, surgical navigation systems have recently been developed, based on anatomical reference frame definitions through landmark digitations and functional calibration. In this study, femoral and tibial resection plane alignments, obtained by conventional tecnique, were measured intraoperatively during total knee replacements by a navigation system to quantify potential errors in conventional bone preparation techniques.

METHODS

Femoral and tibial resection plane alignments, obtained by conventional femoral intramedullary and tibial extramedullary cutting guides, were measured intraoperatively in 25 primary total knee replacements by a navigation system. This system enabled the surgeon to calculate, before definitive bone sawing, the final position and orientation of all resection planes.

RESULTS

The measurements revealed unsatisfactory alignments in nearly all anatomical planes. Except for tibial varus/valgus, final plane orientations were considerably different from those targeted by the surgeon via the navigation system, respectively 7 degrees, 8 degrees and 10 degrees apart in varus-valgus and flexion-extension at the femur, and in flexion-extension at the tibia.

CONCLUSION

Modern computer-aided surgery in total knee replacement, once relevant precision has been established in all femur and tibia anatomical planes, can in the future limit the current critical component misalignments.

Value of information analysis for a new technology: Computer-assisted total knee replacement

Objectives: The aim of this study was to demonstrate how value of information analysis can measure the upper limit on returns to future research and identify the research priorities for computer-assisted total knee replacement (CAS-TKR).

Methods: Using a previous economic analysis of CAS-TKR compared with conventional TKR, the population expected value of perfect information (EVPI) was calculated using Monte Carlo simulation to provide an estimate of the upper limit on returns to future research. The population expected value of partial perfect information (EVPPI) for both individual parameters and groups of parameters was estimated to inform specific future research priorities.

Results: The UK individual EVPI would be £21.4 if the willingness to pay for one QALY (quality-adjusted life-year) were £30,000. The population EVPPI would be £8.3 million, assuming a 10-year time horizon for CAS-TKR. In this instance, the expected value of information is positively related to willingness to pay for one QALY for the range of £0 to £50,000. Although each individual parameter had an EVPPI of £0, groups of utility parameters had positive EVPPI. Population EVPPI was £5.6 million for utility parameters, £20,000 for transition probabilities relating to CAS-TKR, and £5,000 for transition probabilities related to conventional TKR.

Conclusions: The study provides evidence on which parameters further information may be of most value. Focusing research on the utility values associated with health states relating to TKR would be of greatest value.

Automated hydraulic tensor for Total Knee Arthroplasty

To obtain a long lifespan of knee prosthesis, it is necessary to restore the alignment of the lower limb. In some cases of severe arthrosis, the ligament envelope of the joint may be deformed, inducing an asymmetric laxity once the lower limb is realigned. Because there is not yet unanimity regarding how to optimally measure or implement soft tissue balance, we provide a means to acquire a variety of measurements. In traditional surgery, the surgeon sometimes uses a "tensor", which acts like a forceps. This system was redesigned, instrumented, actuated, and integrated into a navigation system for orthopaedic surgery. Improving the perception of the surgeon, it helps him to address the ligament balancing problem. Our first prototype has been tested on sawbones before being validated in an experiment on two cadavers. In our first attempt, the surgeon was able to assess soft tissue balance but judged the device not powerful enough, which led us to develop a new more powerful hydraulic system. In this paper, we present our approach and the first results of the new hydraulic tensor which is currently in an integration process.

A cadaveric study to assess the accuracy of computer-assisted surgery in locating the hip center during total knee arthroplasty

Computer-assisted technology allows the accurate location of inaccessible landmarks such as the center of the hip in total hip arthroplasty. Using 7 fresh normal cadaveric hips, we conducted 2 studies. The first study compared iliac (A) vs no iliac (B) tracking. The second study assessed the reliability of the hip center acquisition using the range of hip motion during manipulation. The first study revealed no statistical difference between the 2 techniques A (mean, 0.67; SD, 0.15) and B (mean, 0.66; SD, 0.32) used to locate the center of the hip. In the second study, a range of motion less than 10 degrees negatively affected accuracy. Using this technology, without an iliac tracker, allows accurate and precise determination of the center of the hip.

Location and number of cortical fixation points and the effect on reference base stability during computer-navigated total knee arthroplasty

This study investigated 2 methods of reference base fixation for computer navigation markers for computer-navigated total knee arthroplasty. Five cadaveric specimens were used to test a 1-pin and 3-pin base system. A navigation system (Stryker Navigation, Kalamazoo, Mich) was used for testing with applied loads and torques to the reference base. Changes in distance from a verification point as well change in alignment were recorded. The change in distance to a reference point as well as the change in alignment data was significantly different at 65 N of applied load with the 3-pin construct being more stable (P = .02). The results suggest that 3-pin fixation in the metaphyseal portion of the distal femur is more stable than a single-pin bicortical construct.

Load balance in total knee arthroplasty: an in vitro analysis

BACKGROUND

One of the goals of total knee arthroplasty (TKA) is to balance the loads between the compartments of the knee. An instrumented load cell that measures compartment loads in real time is utilized to evaluate conventional, qualitative methods of achieving this balance.

METHODS

TKA was performed on 10 cadaveric knees. Prior to and after load balancing, compartment forces were measured at flexion angles of 0-90 degrees. Knees were randomly assigned into one of two groups, based upon whether or not the surgeons could visualize the load cell's output during balancing.

RESULTS

Prior to attempting load balance, there were significant differences between the medial and lateral compartment loads for all knees (p < 0.05). After attempting balance with the aid of the load cell, there was equal load balance at all angles studied. Without the aid of the load cell, balance was not consistently achieved at every angle.

CONCLUSIONS

Conventional load balancing techniques in TKA are not perfect.

[Minimally invasive and navigated implantation for total knee arthroplasty: X-ray analysis and early clinical results]

Total knee arthroplasty (TKA) alignment is one of the most important factors in long-term prosthesis survival. Minimally invasive surgical (MIS) procedures are becoming more common. There may be an increased overall complication rate, especially component malpositioning, due to poor visualisation. The disadvantage of restricted visualisation in the less invasive technique can be compensated by a navigation system. This combined procedure is described in this paper. A total of 40 Search Evolution TKAs were implanted using OrthoPilot navigation in the standard manner, and 40 TKAs were implanted using MIS via a subvastus approach. Primary osteoarthritis of the third or fourth degree, without severe valgus deformity, was the indication. These patients were then selected at random as they came to the institution. The results were evaluated radiologically and clinically.Pain, range of motion, gait and function, and the entire clinical score 10 days after the operation were significantly better in the MIS-group. At 6 and 12 weeks postoperatively, these results were no longer statistically significant. Ideal radiological results were obtained in all cases. No differences in limb axis and component alignment were found after the operation between the navigated groups. MIS is technically very demanding. That is why it should be used only in carefully selected cases. Its advantages occur in the first weeks after the surgery. The long-term results must still be determined.

From scans to sutures: computer-assisted orthopedic surgery in the twenty-first century

Computer-assisted surgery is the process of using medical images, such as CT scans, X-ray fluoroscopy, or 3D ultrasound, to improve patient care. A typical surgical procedure begins by acquiring and processing a CT scan with specially developed image-analysis software. A surgeon then performs a "virtual surgery" on the patient to develop a preoperative plan. In the operating room the medical image is registered to the patient's anatomy by finding an optimal rigid-body transformation. This transformation allows an object or motion in one coordinate frame to be represented in the other frame, and thus a surgeon can visualize the location of an instrument deep within concealed anatomy while avoiding structures at risk. The operating surgeon can also use computer-tracked fluoroscopy or ultrasound for 3D guidance. For the past seven years, our interdisciplinary research group has been investigating fundamental problems in orthopedic surgery of bones and joints. This paper is an overview of the problems and solutions that have been tested in a set of pilot clinical trials in which we have treated more than 250 patients for early or advanced arthritis, poorly healed bone fractures, and treatment of deep bone tumors.

Improving tibial component coronal alignment during total knee arthroplasty with use of a tibial planing device

BACKGROUND

The outcomes of knee arthroplasty have been shown to be affected by component alignment. Intramedullary and extramedullary alignment instrumentation are fairly effective for achieving the desired mean tibial component coronal alignment. However, there are outliers representing >3 degrees of varus or valgus alignment with respect to the anatomic tibial shaft axis. We measured the efficacy of a custom tibial planing device for reducing the outliers in tibial alignment.

METHODS

We designed a tibial planing tool in an effort to improve tibial alignment. In one cohort (100 knees), we used traditional intramedullary alignment instrumentation to make the tibial bone cut. In a second cohort (120 knees), we used intramedullary alignment instrumentation to make the cut and also used a custom tool to check the cut and to correct an inexact cut. Tibial tray alignment relative to the long axis of the tibial shaft was measured in the coronal and sagittal planes on postoperative radiographs. The target coronal alignment was 90 degrees with respect to the tibial shaft axis (with <90 degrees denoting varus alignment). A total of 100 anteroposterior radiographs and sixty-five lateral radiographs were analyzed for the group that was treated with traditional instrumentation alone, and a total of 120 anteroposterior radiographs and fifty-five lateral radiographs were analyzed for the group that was treated with use of the custom tibial planing device.

RESULTS

The mean coronal alignment of the tibial component was 89.5 degrees +/- 2.1 degrees in the group that was treated with traditional instrumentation alone and 89.6 degrees +/- 1.4 degrees in the group that was treated with use of the custom planing device. Although the mean coronal alignment was not significantly different, the number of outliers was substantially reduced when the custom planing device was used. All 120 components that had been aligned with use of the custom planing device were within 3 degrees of the target coronal alignment, compared with only eighty-seven of the 100 components that had been implanted with use of traditional intramedullary alignment alone (p = 0.05).

CONCLUSIONS

The use of a simple, inexpensive tibial planing device reduced the number of outliers due to tibial tray malalignment. Tibial varus has been associated with a higher risk of failure. Improving the accuracy of tibial component alignment may reduce the potential for poor clinical outcomes.

[The history and development of computer assisted orthopaedic surgery]

Computer assisted orthopaedic surgery (CAOS) was developed to improve the accuracy of surgical procedures. It has improved dramatically over the last years, being transformed from an experimental, laboratory procedure into a routine procedure theoretically available to every orthopaedic surgeon. The first field of application of computer assistance was neurosurgery. After the application of computer guided spinal surgery, the navigation of total hip and knee joints became available. Currently, several applications for computer assisted surgery are available. At the beginning of navigation, a preoperative CT-scan or several fluoroscopic images were necessary. The imageless systems allow the surgeon to digitize patient anatomy at the beginning of surgery without any preoperative imaging. The future of CAOS remains unknown, but there is no doubt that its importance will grow in the next 10 years, and that this technology will probably modify the conventional practice of orthopaedic surgery.

Surgical navigation for total knee arthroplasty: A perspective

A new generation of surgical tools, known as surgical navigation systems, has been developed to help surgeons install implants more accurately and reproducibly. Navigation systems also record quantitative information such as joint range of motion, laxity, and kinematics intra-operatively. This article reviews the history of surgical navigation for total knee arthroplasty, the biomechanical principles associated with this technology, and the related clinical research studies. We describe how navigation has the potential to address three main challenges for total knee arthroplasty: ensuring excellent and consistent outcomes, treating younger and more physically active patients, and enabling less invasive surgery.

Navigation in total knee arthroplasty. A multicenter study

We carried out a multicentre study to compare the postoperative femorotibial radiographic axis in two total knee replacement groups; one using manual instrumentation and the other using navigation. In the latter group, three navigation systems were used: Stryker, Orthopilot and Navitrack. The prior circumstances of patients in terms of age, weight, aetiology, epicondylar perimeter, patellar tendon length and knee deformity was similar in both groups. The duration of the operation was longer in the group with navigation (16.7 min). A normal femorotibial axis was more frequently obtained in the group with a navigator compared to the manual group (48.1% and 30%, respectively). A varus axis was most common in the manual group (42.2 and 26.9%, respectively). When we analysed the final postoperative radiographic axis, taking 180 degrees to be a normal result, we noted that cases where manual instrumentation was used deviated by 1.19 degrees more than those carried out with navigation, with this difference being statistically significant (P<0.001). No significant differences were found in the final angle of the extremity with the different navigation systems. The navigation systems used in this study improve the frontal angle of the arthroplasty.

Experiences with computer navigated total knee arthroplasty

The successful outcome of total knee arthroplasty (TKA) is very much dependent on precise positioning of the components. Inaccuracy may result in complaints as well as in early mechanical failure. Between March 2003 and September 2005, 69 TKA procedures were performed by the computer navigated technique. The postoperative outcome of this cohort was compared with the same number of TKAs done by the traditional technique. The lower limb anatomical axis was determined in all cases pre- and postoperatively by weight-bearing anteroposterior (AP) and lateral full length X-rays. The positions of femoral and tibial components were recorded. Comparing the data in the navigation group on the AP view, 96.6% of femoral and 96.9% of tibial components and on the lateral view in 95.4% of femoral and in 95.4% of tibial components, the overall postoperative axis in 95.4% fell in the range considered in the literature as optimal. In the traditional group on the AP view, 75.7% of femoral and 68.1% of tibial components and on the lateral view 81.8% of femoral and 63.6% of tibial components, the overall postoperative axis in 60.6% fell between the values considered optimal in the literature. It seems to be proven that the computer navigated total knee arthroplasty technique ensures positioning of components significantly more precisely compared with the traditional surgical method. Accuracy of navigation depends on the software used, on the correct detection of anatomical reference points, and on a potentially uneven thickness of the cement layer during final insertion of the components. The computer navigated technique does not substitute professional skill and experience, since it merely transmits information for the surgeon. The decision is in the hands of the doctor during the entire procedure. The real benefits of the computer navigated technique require further research and can be determined only after long-term analyses.

The high variability of tibial rotational alignment in total knee arthroplasty

Although various techniques are advocated to establish tibial rotational alignment during total knee arthroplasty, it is unknown which is most repeatable. We evaluated the precision and accuracy of five tibial rotational alignment techniques to determine whether computer-assisted navigation systems can reduce variability of tibial component rotational alignment when compared to traditional instrumentation. Eleven orthopaedic surgeons used four computer-assisted techniques that required identification of anatomical landmarks and one that used traditional extramedullary instrumentation to establish tibial rotational alignment axes on 10 cadaver legs. Two computer-assisted techniques (axes between the most medial and lateral border of the tibial plateau, and between the posterior cruciate ligament [PCL] and the anterior tibial crest) and the traditional technique were least variable, with standard deviations of 9.9 degrees, 10.8 degrees, and 12.1 degrees, respectively. Computer-assisted techniques referencing the tibial tubercle (axes between the PCL and the medial border or medial 1/3 of the tubercle) were most variable, with standard deviations of 27.4 degrees and 28.1 degrees. The axis between the medial border of the tibial tubercle and the PCL was internally rotated compared to the other techniques. None of the techniques consistently established tibial rotational alignment, and navigation systems that establish rotational alignment by identifying anatomic landmarks were not more reliable than traditional instrumentation.

Is restricted femoral navigation sufficient for accuracy of total knee arthroplasty?

A total knee arthroplasty performed with navigation results in more accurate component positioning with fewer outliers. It is not known whether image-based or image-free-systems are preferable and if navigation for only one component leads to equal accuracy in leg alignment than navigation of both components. We evaluated the results of total knee arthroplasties performed with femoral navigation. We studied 90 knees in 88 patients who had conventional total knee arthroplasties, image-based total knee arthroplasties, or total knee arthroplasties with image-free navigation. We compared patients' perioperative times, component alignment accuracy, and short-term outcomes. The total surgical time was longer in the image-based total knee arthroplasty group (109 +/- 7 minutes) compared with the image-free (101 +/- 17 minutes) and conventional total knee arthroplasty groups (87 +/- 20 minutes). The mechanical axis of the leg was within 3 degrees of neutral alignment, although the conventional total knee arthroplasty group showed more (10.6 degrees ) variance than the navigated groups (5.8 degrees and 6.4 degrees , respectively). We found a positive correlation between femoral component malalignment and the total mechanical axis in the conventional group. Our results suggest image-based navigation is not necessary, and image-free femoral navigation may be sufficient for accurate component alignment.

Grundlagen der computerassistierten Chirurgie

Using navigation systems in general orthopaedic surgery and, in particular, knee replacement is becoming more and more accepted. This paper describes the basic technological concepts of modern computer assisted surgical systems. It explains the variation in currently available systems and outlines research activities that will potentially influence future products. In general, each navigation system is defined by three components: (1) the therapeutic object is the anatomical structure that is operated on using the navigation system, (2) the virtual object represents an image of the therapeutic object, with radiological images or computer generated models potentially being used, and (3) last but not least, the navigator acquires the spatial position and orientation of instruments and anatomy thus providing the necessary data to replay surgical action in real-time on the navigation system's screen.

Effect of one- and two-pin reference anchoring systems on marker stability during total knee arthroplasty computer navigation

OBJECTIVE

This study investigated different infrared marker reference base attachments in cadaveric bone and their effects on alignment outcome when different loads were applied.

MATERIAL AND METHODS

Five cadaveric specimens were used to test four reference base attachments: a locking one-pin (4.0 mm and 5.0 mm pins) and a two-pin clamp (Hoffman fixator, 3.0 mm and 5.0 mm pins, Stryker Inc., NJ). Each was tested with metaphyseal and diaphyseal attachments. A navigation system (Stryker Navigation, MI) was used for testing with applied incremental loads and torques (65 N and 1.0 Nm) to the different reference base configurations.

RESULTS

With 65 N the maximum change in distance to a verification point was 4.3 + 1.6 mm with the 4.0 mm locking pin in metaphyseal bone. No difference in verification point distances was found with any two-pin configuration. Alignment changes greater than 4 degrees resulted with the 65 N loads and a 4.0 mm pin.

CONCLUSION

The results may prove beneficial in comparing the resulting error of different manufacturers and allow surgeons to realize the variability that may occur through incidental contact in the operating room.

Kinematic navigation in total knee replacement--experience from the first 50 cases

BACKGROUND/PURPOSE

Proper alignment of the prosthesis is critical in total knee replacement (TKR) to minimize long-term wear, risk of osteolysis, and loosening of the prosthesis. This study examined the accuracy of lower limb alignment obtained using a kinematic navigation system for TKR, and the extra time needed to adopt this system.

METHODS

From August 2002 to April 2003, 71 patients with knee osteoarthritis underwent 79 primary TKR operations by the same surgical team. Fifty of these operations were performed with the aid of the CT-free kinematic navigation system, and the remaining 29 were performed with conventional manual methods. Results, including operation time, radiographic alignment of the prosthesis and complications, for the two groups were compared.

RESULTS

Patients in the kinematic navigation group achieved better accuracy in the coronal plane than the conventional group in terms of postoperative mechanical axis (1.89 +/- 0.63 degrees vs. 3.38 +/- 1.07 degrees ). Less variation was noted in the navigation group (femur: SD 1.88 degrees vs. 7.12 degrees ; tibia: SD 1.54 degrees vs. 2.99 degrees ), although the difference in the mean values was not significant (p = 0.475 and 0.55, respectively). The operation time (from skin to skin) in the navigation group (100.6 +/- 4.3 minutes) was longer than that in the conventional group (92.7 +/- 5.1 minutes; p = 0.027). Two perioperative fractures occurred in the navigation group, both of which were attributed to patient factors as opposed to operation procedures. No major complications such as infection or pulmonary embolism occurred during this study.

CONCLUSION

Use of a kinematic navigation system in TKR provides better accuracy than conventional manual methods. The technique is easy to use, has a short learning curve, and requires an additional operation time of less than 10 minutes. Precise alignment can be achieved with the aid of navigation in most cases.

Intraoperative passive kinematics of osteoarthritic knees before and after total knee arthroplasty

Total knee arthroplasty is a successful procedure to treat pain and functional disability due to osteoarthritis. However, precisely how a total knee arthroplasty changes the kinematics of an osteoarthritic knee is unknown. We used a surgical navigation system to measure normal passive kinematics from 7 embalmed cadaver lower extremities and in vivo intraoperative passive kinematics on 17 patients undergoing primary total knee arthroplasty to address two questions: How do the kinematics of knees with advanced osteoarthritis differ from normal knees?; and, Does posterior substituting total knee arthroplasty restore kinematics towards normal? Osteoarthritic knees displayed a decreased screw-home motion and abnormal varus/valgus rotations between 10 degrees and 90 degrees of knee flexion when compared to normal knees. The anterior-posterior motion of the femur in osteoarthritic knees was not different than in normal knees. Following total knee arthroplasty, we found abnormal varus/valgus rotations in early flexion, a reduced screw-home motion when compared to the osteoarthritic knees, and an abnormal anterior translation of the femur during the first 60 degrees of flexion. Posterior substituting total knee arthroplasty does not appear to restore normal passive varus/valgus rotations or the screw motion and introduces an abnormal anterior translation of the femur during intraoperative evaluation.

Early assessment of the likely cost-effectiveness of a new technology: A Markov model with probabilistic sensitivity analysis of computer-assisted total knee replacement

OBJECTIVES

The objective of this study is to apply a Markov model to compare cost-effectiveness of total knee replacement (TKR) using computer-assisted surgery (CAS) with that of TKR using a conventional manual method in the absence of formal clinical trial evidence.

METHODS

A structured search was carried out to identify evidence relating to the clinical outcome, cost, and effectiveness of TKR. Nine Markov states were identified based on the progress of the disease after TKR. Effectiveness was expressed by quality-adjusted life years (QALYs). The simulation was carried out initially for 120 cycles of a month each, starting with 1,000 TKRs. A discount rate of 3.5 percent was used for both cost and effectiveness in the incremental cost-effectiveness analysis. Then, a probabilistic sensitivity analysis was carried out using a Monte Carlo approach with 10,000 iterations.

RESULTS

Computer-assisted TKR was a long-term cost-effective technology, but the QALYs gained were small. After the first 2 years, the incremental cost per QALY of computer-assisted TKR was dominant because of cheaper and more QALYs. The incremental cost-effectiveness ratio (ICER) was sensitive to the "effect of CAS," to the CAS extra cost, and to the utility of the state "Normal health after primary TKR," but it was not sensitive to utilities of other Markov states. Both probabilistic and deterministic analyses produced similar cumulative serious or minor complication rates and complex or simple revision rates. They also produced similar ICERs.

CONCLUSIONS

Compared with conventional TKR, computer-assisted TKR is a cost-saving technology in the long-term and may offer small additional QALYs. The "effect of CAS" is to reduce revision rates and complications through more accurate and precise alignment, and although the conclusions from the model, even when allowing for a full probabilistic analysis of uncertainty, are clear, the "effect of CAS" on the rate of revisions awaits long-term clinical evidence.

Computer-assisted patellofemoral arthroplasty: a mechanism for optimizing rotation

We reviewed the early outcome of 4 primary Avon patellofemoral arthroplasties performed by a single surgeon in a 1-year period. All operations were performed to treat symptomatic osteoarthritis, which had failed conservative management. All 4 procedures were performed with intraoperative computer navigation to enable correct alignment of the prosthesis. The patients were assessed clinically using the Oxford knee score and Crosby and Insall score. Radiologically, they were assessed using plain radiographs and computed tomography long leg and dynamic axial alignment views of the prosthesis. All patients had excellent early clinical and radiological results proving intraoperative navigation produces safe, reliable, and reproducible implant position in patellofemoral arthroplasty.

Computer-assisted total knee arthroplasty using patient-specific templating

Current techniques used for total knee arthroplasty rely on conventional instrumentation that violates the intramedullary canals. Accuracy of the instrumentation is questionable, and assembly and disposal of the numerous pieces is time consuming. Navigation techniques are more accurate, but their broad application is limited by cost and complexity. We aimed to prove a new concept of computer-assisted preoperative planning to provide patient-specific templates that can replace conventional instruments. Computed tomography-based planning was used to design two virtual templates. Using rapid prototyping technology, virtual templates were transferred into physical templates (cutting blocks) with surfaces that matched the distal femur and proximal tibia. We performed 45 total knee arthroplasties on 16 cadaveric and 29 plastic knees, including a comparative trial against conventional instrumentations. All operations were performed using patient-specific templates with no conventional instrumentations, intramedullary perforation, tracking, or registration. The mean time for bone cutting was 9 minutes with a surgical assistant and 11 minutes without an assistant. Computer-assisted analyses of six random computed tomography scans showed mean errors for alignment and bone resection within 1.7 degrees and 0.8 mm (maximum, 2.3 degrees and 1.2 mm, respectively). Patient-specific templates are a practical alternative to conventional instrumentations, but additional clinical validation is required before clinical use.

Praxiteles: a miniature bone-mounted robot for minimal access total knee arthroplasty

We have been working to develop a compact, accurate, safe, and easy-to-use surgical robot for minimally invasive total knee arthroplasty (TKA). The goal of our bone-mounted robot, named Praxiteles, is to precisely position a surgical bone-cutting guide in the appropriate planes surrounding the knee, so that the surgeon can perform the planar cuts manually using the guide. The robot architecture is comprised of 2 motorized degrees of freedom (DoF) whose axes of rotation are arranged in parallel, and are precisely aligned to the implant cutting planes with a 2 DoF adjustment mechanism. Two prototypes have been developed and tested on saw bones and cadavers--an initial one for open TKA surgery and a new version for MIS TKA, which mounts on the side of the knee. A novel bone-milling technique is also presented that uses passive guide and a side milling tool.

Evaluation of a new algorithm to determine the hip joint center

Accurately locating the hip joint center is a challenging and important step in many biomechanical investigations. The purpose of this study was to test the accuracy and robustness of a "pivoting" algorithm used to locate the hip center. We tested the performance of this algorithm with data acquired by manipulating a ball and socket model of the hip through several motion patterns. The smallest mean errors of 2.2+/-0.2 mm occurred with a circumduction motion pattern, while the largest errors of 4.2+/-1.3 mm occurred with single-plane motion (e.g., flexion/extension). Introducing random noise with an amplitude of 30 mm increased the errors by only 1.3+/-0.5 mm with a circumduction motion pattern. The pivoting algorithm performs well in the laboratory, and further work is warranted to evaluate its performance in a clinical setting.

Reproducibility of intra-operative measurement of the mechanical axes of the lower limb during total knee replacement with a non-image-based navigation system

OBJECTIVE

The restoration of a normal mechanical axis of the lower limb following total knee prosthesis (TKP) depends on the accuracy of the intra-operative measurement of the femoro-tibial angle. We have studied the reproducibility of intra-operative measurement of the coronal mechanical femoro-tibial axis with the OrthoPilot (Aesculap, Tuttlingen, Germany) non-image-based navigation system.

MATERIAL AND METHODS

A consecutive series of 20 TKP (Aesculap SEARCH Evolution prosthesis) implanted by the same surgical team of two senior orthopedic surgeons was analyzed. They used a non-image-based navigation system that allows the mechanical axes of the femur and tibia to be defined with a kinematic analysis. The operating surgeon and assistant surgeon performed the kinematic analysis twice and once, respectively, and measured coronal mechanical femoro-tibial angles in maximal extension and at 90 degrees flexion without varus or valgus stress.

RESULTS

The mean intra-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.1 degrees (SD = 0.7 degrees). The mean intra-observer variation in the measurement of the coronal mechanical femoro-tibial angle at 90 degrees of knee flexion was 0.2 degrees (SD = 0.6 degrees). The mean inter-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.1 degrees (SD = 0.7 degrees). The mean inter-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.0 degrees (SD = 0.6 degrees). There were no significant differences and a high correlation between all paired intra- and inter-observer measurements.

CONCLUSION

This system allows high reproducibility of the intra-operative measurement of the mechanical axes of the lower limb by a non-image-based kinematic registration of the hip, knee and ankle centers.

Computer navigation versus standard instrumentation for TKA: a single-surgeon experience

Component alignment errors in total knee arthroplasty greater than 3 degrees can be associated with poorer outcomes. This retrospective study seeks to determine if computer navigation can improve accuracy of component alignment in comparable patient populations. The efficiency and safety of the navigated technique is also evaluated. Fifty total knee arthroplasties done using an imageless navigation system and 50 cases using standard instrumentation were compared. The same surgeon used a single system (Zimmer-Natural Knee) in all cases. Long-standing radiographs collected at 6-week followup were measured for component orientation. When the navigation system was used 98% (49 of 50 cases) of all femoral components and 100% (50 of 50 cases) of all tibial components were placed within +/- 3 degrees of the radiographic goal position. There was a decrease in the standard instrumentation group to 90% (45 of 50 cases) and 92% (46 of 50 cases) within +/- 3 degrees , respectively. There was a difference in the standard deviations observed for the navigated cases and the conventional cases when femoral and tibial component position was considered. Average tourniquet time was 68 minutes in the navigated group and 57 minutes in the conventional group. There were no technique specific complications associated with the navigation system. This system affords the surgeon the potential to reduce outliers with regard to component position without an increase in complications. Tourniquet times were increased with the use of the computer.

LEVEL OF EVIDENCE

Therapeutic study, Level III-1 (retrospective comparative study). See the Guidelines for authors for a complete description of levels of evidence.

Evaluation of methods that locate the center of the ankle for computer-assisted total knee arthroplasty

Accurate alignment of the mechanical axis of the limb is important to the success of a total knee arthroplasty. Although computer-assisted navigation systems can align implants more accurately than traditional mechanical guides, the ideal technique to determine the distal end point of the mechanical axis, the center of the ankle, is unknown. In this study, we evaluated the accuracy, precision, objectivity, and speed of five anatomic methods and two kinematic methods for estimating the ankle center in 11 healthy subjects. Magnetic resonance images were used to characterize the shape of the ankle and establish the true ankle center. The most accurate and precise anatomic method was establishing the midpoint of the most medial and most lateral aspects of the malleoli (4.5 +/- 4.1 mm lateral error; 2.7 +/- 4.5 mm posterior error). A biaxial model of the ankle (2.0 +/- 6.4 mm medial error; 0.3 +/- 7.6 mm anterior error) was the most accurate kinematic method. Establishing the midpoint of the most medial and most lateral aspects of the malleoli was an accurate, precise, objective, and fast method for establishing the center of the ankle.

Navigated unicompartmental knee replacement

The author developed a non-image-guided navigation system for unicompartmental knee replacement that can be used with conventional surgery or minimally invasive surgery. The author performed a radiological analysis of the accuracy of implantation for unicompartmental knee replacement with conventional surgery, navigated minimally invasive surgery, and conventional navigated surgery. A significant increase in the rate of prostheses implanted in the desired angular range for all criteria in conventional navigated minimally invasive surgery and conventional navigated surgery was found. The conventional navigated technique was significantly more accurate than minimally invasive surgery.

Minimally invasive navigated knee surgery: an American perspective

Minimally invasive total knee replacement surgery may make it possible for patients to undergo the procedure with less pain and recover from the surgery more quickly than has been previously possible. However, minimally invasive techniques have the potential for being associated with a number of complications, including implant and limb malalignment. Computer-assisted technologies used in conjunction with minimally invasive techniques allow the accuracy with which the procedures are performed to be retained.

Consistency of implantation of a total knee arthroplasty with a non-image-based navigation system: a case-control study of 235 cases compared with 235 conventionally implanted prostheses

The aim of the study was to assess the consistency of the non-image-based navigation system OrthoPilot, Aesculap, Tuttlingen, Germany, in total knee arthroplasty (TKA) implantation in 5 European centers. Two hundred thirty-five TKAs implanted with this navigation system were matched (according to severity of the preoperative coronal deformation and body mass index) to a historical control group of 235 TKAs implanted with a conventional technique. Consistency of implantation was studied on a 3-month postoperative radiological control with coronal long-leg and sagittal standard x-rays. The use of the OrthoPilot navigation system allowed a statistically significant improvement in the consistent placement of both tibial and femoral components. In accordance with current literature, survival of the navigated implanted prostheses is expected to be longer.

Computer assisted navigation in total knee arthroplasty: improved coronal alignment

The use of a computer navigation system is intended to optimize implant positioning. This study compares prospectively followed total knee arthroplasty (TKA) done with imageless computer-assisted navigation with a cohort of TKA done with manual instruments. Primary TKAs were performed on 147 knees, with 78 in the manual group and 69 in the navigated group. Coronal alignment was determined by postoperative full-length standing radiographs. The 2 groups had similar mean values for radiographic mechanical axis at 0.4 degrees . There was a larger variation in alignment in the manual group, with 58% of the manual group within 2 degrees of neutral compared with 78% of the navigated group (P = .008). The navigation system reproducibly resulted in a more reliable reproduction of the mechanical axis.

Intraobserver errors in obtaining visually selected anatomic landmarks during registration process in nonimage-based navigation-assisted total knee arthroplasty: a cadaveric experiment

This study investigated the intraobserver errors in obtaining visually selected anatomic landmarks that were used in registration process in a nonimage-based computer-assisted total knee replacement (TKR) system. The landmarks studied were center of distal femur, medial and lateral femoral epicondyle, center of proximal tibia, medial malleolus, and lateral malleolus. Repeated registration in the above sequence was done for 100 times by a single surgeon. The maximum combined errors in the mechanical axis of the lower limb were only 1.32 degrees (varus/valgus) in the coronal plane and 4.17 degrees (flexion/extension) in the sagittal plane. The maximum error in transepicondylar axis was 8.2 degrees. The errors using the visual selection of anatomic landmarks for the registration technique of bony landmarks in nonimage-based navigated TKR did not introduce significant error in the mechanical axis of the lower limb in the coronal plane. However, the error in the transepicondylar axis was significant in the "worst-case scenario."

Leg axis after computer-navigated total knee arthroplasty: a prospective randomized trial comparing computer-navigated and manual implantation

To compare the alignment after computer-navigated total knee arthroplasty, 52 patients were randomly allocated to 2 groups. Twenty-seven patients received a total knee arthroplasty with the aid of a kinematic computer-navigation system, and 25 patients received a total knee arthroplasty with the conventional method. Both groups were well balanced concerning demographic data and preoperative scores. At 3-month follow-up, the mechanical alignment of the leg reached the desired straight axis in more cases with the computer-navigated implantation. This difference was statistically significant. The femoral and tibial mechanical anteroposterior axis and the femoral and tibial sagittal tilt (slope) measured on sagittal x-rays were not significantly improved in this patient group.